A phase locked loop (PLL) is a frequency feedback circuit which generates an output signal having desired frequency and phase in response to a reference signal (clock signal) input from the outside, and has been frequently used for a frequency synthesis circuit, a clock recovery circuit, or the like.
FIG. 1 is a diagram illustrating a schematic configuration of a charge pump type PLL as one example of a PLL in the related art.
Referring to FIG. 1, a charge pump type PLL 100 in the related art includes a phase frequency detector (PFD) 110, a charge pump (CP) 120, a loop filter 130, and a voltage control oscillator 140.
The PFD 110 compares a reference signal with a feedback signal to output a phase difference signal. The CP 120 supplies charges in proportion to a pulse width of a phase difference signal and the loop filter 130 varies the voltage with a change in accumulated charge amount. The voltage control oscillator 140 outputs a specific frequency based on a varied voltage, that is, a control voltage. The signal output from the voltage control oscillator 140 is fed-back to be input to the PFD 110. Generally, the PFD 110 compares rising edge of the reference signal with rising edge of the feedback signal or falling edge of the reference signal with falling edge of the feedback signal, and outputs a signal proportional to the phase difference.
Further, the PLL 100 may additionally provide a frequency divider (not illustrated). The frequency divider (not illustrated) is positioned on a feedback route and divides a frequency of an output signal output from the voltage control oscillator 140.
In the PLL in the related art, in order to improve phase and frequency detection speeds, a bandwidth of the PLL needs to be widened. However, in the PLL, in order to secure stability of the PLL due to a kind of sampling operation for detecting the phase difference in the rising edge or the falling edge of the reference signal and the feedback signal, the bandwidth of the PLL is generally limited to 1/10 or less of the reference signal frequency.